**6.2. Heavy metals**

138 New Approaches to the Study of Marine Mammals

Dumping at sea, e.g. dredge spoil.

Offshore exploration, e.g. oil exploration platforms.

**6.1. Human waste into the marine ecosystem** 

*E. coli, Shigella* and gastroenteritis of unknown origin.

Waste from ships, oil spills and the discharge of ballast water, as well as other waste.

There are 33 megacities in the world, and 21 of them are situated on coastlines. If one considers that at least 50% of the world's population lives in urban areas, where wastewater management systems are often outdated or completely inadequate, the sensitive urban coastal ecosystems are under serious threat [66]. It is estimated that over 90% of wastewater in developing countries is discharged, without any form of treatment into the marine environment, as well as into rivers and lakes. In more developed countries, at least primary treatment is required before discharging wastewater into the environment. Consequently, millions of litres of raw waste water or digested sludge are released into the marine environment. This practice often represents an alternative to tertiary treatment, as well as the most inexpensive means of disposal. The effluents released in ocean outfalls contain faecal material from domestic waste water and industrial discharges with persistent toxic substances and heavy metals. Harmful impacts include risk to public health, beaches, marine animals, as well as contamination of shellfish. Moreover, this release of high volumes of organic matter into the marine environment or contributory rivers also results in eutrophication, which leads to so-called dead zones in the seas and oceans. Approximately 245 000 km2 of marine environment is thought to be affected by these dead zones [66, 69].

Bitton's [69] book summarized several global surveys of enteric pathogens in contaminated sea water. A number of authors reported enteric viruses of the coast of countries such as Brazil, France, Israel, Italy, Spain and the USA. The virus types found included polioviruses, coxsackie A and B viruses, echo-, adeno- and rotaviruses. These were also detected in sediments in close proximity of sewage outfalls, and found to prevail for extended periods of time. Also, pathogenic bacteria such as *Salmonella* and *Vibrio cholerae* were reported in coastal waters near ocean outfalls. Several illnesses among the human population have been reported as a result of exposure to bacteria from sewage contaminated water, including spp. of *Aeromonas, Leptospira, Mycobacterium, Legionella, Pseudomonas, Vibrio* and *Staphylococcus.*  Adenoviruses were also associated with these illnesses, as well as the protozoa, *Naegleria fowleri* and *Acanthamoeba.* These microbes were found in cases of wound infections, skin and subcutaneous lesions, dermatitis, subcutaneous abscesses, septicaemia, conjunctivitis, pharyngitis, meningoencephalitis, Legionnaire's disease and ear infections. Outbreaks of gastroenteritis, on the other hand, were attributed to *Giardia* and *Cryptosporidium,* as well as

Some autochthonous microbes have also been documented as agents of disease among humans. *Pseudomonas aeruginosa,* for example, had been reported in immuno-compromised patients, and was also detected in high numbers in faecal polluted recreational waters [69]. Utilizing such recreational areas, was found not only to be associated with enteric diseases, but also with upper respiratory infections. Cases of pneumonia have been attributed to Heavy metals are metallic chemical elements with a relatively high density and are also known as 'toxic metals'. This group includes elements such as copper (Cu), zinc (Zn), lead (Pb), mercury (Hg), nickel (Ni), cobalt (Co), arsenic (As), thallium (Tl) and chromium (Cr). These metals are common components of the earth's crust and occur naturally in ecosystems at different concentrations. However, the bio-available concentrations of these elements have increased significantly over time since the dawn of the Industrial Revolution. The resulting bio-accumulation of these metals has reached critical levels in many ecosystems. These elements enter the water supply through industrial and consumer waste, or acidic rain that in turn causes chemical reactions in soil releasing the metals into streams, rivers and ground water. Additional sources include waste from chemical, electro-plating, tanning, smelting and especially the mining industry [70]. Previously, the lead added to motor fuels as an anti-knock agent was released on large scale into the atmosphere in exhaust fumes with a substantial proportion settling on road surfaces. Run-off water from these surfaces therefore contained high levels of lead. Urbanized and heavy industrialized areas are consequently the foci of heavy metal pollution [71].

Living organisms require small amounts of certain heavy metals or trace elements for normal metabolic processes, in the form of co-factors in enzymes. Some heavy metals such as Cd, As, Pb and Hg pose the biggest threat to the health of humans and animals, and daily intake of these metals are toxic and often fatal. Long-term exposure of humans to As in drinking water for example, had been reported to cause increased risk to skin and other types of cancer, as well as other skin lesions including hyperkeratosis and pigmentation anomalies. Similarly, Cd exposure is associated with kidney damage and increased incidence of bone fractures [70]. Marine mammals often occupy the top levels of marine food chains, and therefore, heavy metals accumulate in these animals [72]. In water, heavy

metals may be found in solution in the water column, as colloids, as suspended particles or absorbed to particulate matter [71]. The latter form often ends up as a constituent of the sediment and at least a portion is released again into the water column. It is also important to realize and take into account that not all sources of heavy metals are anthropogenic. The Mediterranean Sea for example is known for its natural high levels of Hg, and likewise the Arctic Sea for higher cadmium (Cd) concentrations [72]. Furthermore, different organs tend to accumulate different heavy metals, and are therefore metal specific. Heavy metals enter cetaceans through their lungs, skin (absorption), from the mother during gestation, through milk during nursing, as well as by ingestion of sea water and food. Also, mysticetes seem to be less affected by heavy metal accumulation as a result of their position in the food chain, when compared to odontocetes that occupy the top level. Interestingly, heavy metal levels are higher in older individuals and nonbreeding females. All these factors should be taken into account in studies on the effects of these metals on marine mammals.

Cutaneous Lesions in Cetaceans: An Indicator of Ecosystem Status? 141

 POPs have adverse effects in human and animal tissue even at very low concentrations. Some of these compounds disrupt normal biological functions, including hormone and

 POPs have a low water and high lipid solubility, resulting in bio-accumulation in the fatty tissue of living organisms and cannot be excreted readily. Also, bio-magnification occurs causing an accumulation effect by factors of many thousands or even millions, as

These chemical compounds are primarily products and by-products of industrial processes, synthetic chemical manufacturing and waste incineration ([80, 81]. Their existence dates back to the industrial boom after World War II, but are currently ubiquitous, and are found in food as well as soil, the atmosphere and various water bodies. In 2001, the United Nations Environment Program (UNEP) completed global negotiations with the signing of the socalled Stockholm convention on banning certain POPs, collectively known as the 'dirty dozen'. During this assessment, certain criteria for the identification and listing of chemicals under the convention were identified. New POPs that were identified during the survey include butylated tin, methylated mercury and polyaromatic hydrocarbon (PAH), as well as other less studied compounds such as chlorinated paraffin's, brominated diphenyl ethers

The big concern caused by organo-chlorines is because of growing evidence that these compounds act as endocrine disruptors [79, 83]. The U.S. EPA [83] report defined endocrine disruptors as 'exogenous agents that interfere with the synthesis, secretion, transport, binding, action or elimination of natural hormones in the body that are responsible for the maintenance of homeostasis, reproduction, development and/or behaviour'. The science of endocrine disruption is still very new (only about 2 decades) and long term studies with effect results are therefore still preliminary [80]. The hormone disrupting effects differ according to the exposure situation and depend on the relative occurrence of the active congeners, specifically on the trophic level from which the food originates. For example, contaminants in the marine food chain of the Arctic Inuit population follow a very long passage. The result is that the higher, slowly metabolized, higher chlorinated PCBs will dominate over the lower chlorinated and more readily metabolized congeners. This situation will therefore create a specific effect on the hormonal balance, which will be different from other populations exposed more directly to the sources of these contaminants [76]. Toxic contaminants can also act as causal or aggravating factors in the development of a range of metabolic disorders. Several studies reported a correlation between metabolic disorders such as diabetes and cardiovascular disease, and lipid adjusted serum levels of substances like PCBs and dioxins. At present, 80% of the adult Greenlandic human population has PCB serum values in excess of 10 µg/l; a concentration shown to cause increased incidences of diabetes. Processes related to the development of metabolic disorders in which toxic contaminants may play an aggravating role include: (1) Proinflammatory effect through the formation of pro-inflammatory cytokines, oxidative stress and/or the formation of reactive oxygen species, (2) modulation of fatty acid metabolism, (3) influence on nuclear receptors, (4) effects on steroidogenesis, and (5) influence on uric acid

other chemical messengers leading to metabolic conditions [79];

these compounds move up food chains [74, 77, 80, 82].

and other flame retardants.

levels [76].

A recent multi-factorial study [73] on mass stranded sperm whales (*Physeter macrocephalus*) revealed relatively high levels of environmental pollutants, including organic Hg (MeHg), Se, Cd, with a Hg:Se ratio of 1:1. Also, opportunistic bacteria cultured from selected organs included representatives of *Vibrio*, *Aeromonas hydrophila* and *Enterococcus*. The authors concluded that these whales were presumably starved causing the mobilization of lipophilic contaminants which accumulated in the adipose tissue. These chemical compounds entered the blood circulation causing immuno- and neurotoxic effects which led to impaired orientation and space perceptions in these sperm whales [73].
